Terahertz phononic crystal in plasmonic nanocavity

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies.A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency(~THz).However,the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light.Here,we design a system that combines Ag nanocav-ity with GaAs/AlAs phononic superlattices,where phonons with the frequency of 4.2 THz can be confined in a pillar with~4 nm diameter.The Q_(c)/V reaches 0.22 nm^(-3),which is~80 times that of the photonic crystal(PhC)nanobeam and~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity,where Q_(c) is optical quality factor and V is mode volume.The optome-chanical single-photon coupling strength can reach 12 MHz,which is an order of magnitude larger than that of the PhC nanobeam.In addition,the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg,which is much smaller than the PhC nanobeam.The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics,quantum information,and terahertz-light transducer.

Experimental investigation on DBD plasma reforming hydrocarbon blends

To improve the‘detonation-supporting’performance of fuel-rich catalytic combustion products,DBD plasma,stimulated by adjustable nanosecond pulse power supply,was used to further regulate the components and concentrations of the hydrocarbon blends.In this paper,the parameters including load voltage,frequency,rising(falling)edge,pulse width and feeding flow rate were changed respectively,and the corresponding concentration and proportion change of the components in blend gas were investigated.According to the experiment result,it was found that when the discharge frequency is low,the plasma mainly promotes the transformation of light gaseous substances,while it mainly promotes the conversion to heavy hydrocarbons when the frequency is larger.Increasing load voltage will strengthen this trend.The controlling and reforming effect of plasma on the blend gas will decrease with the increase of voltage rising(falling)edge and the feeding flow rate.The regulation effect will be strengthened with the increase of pulse width under 200 ns.With the increase of discharge intensity,the‘carbon’settles on the walls of the reactor,which will change the dielectric constant,leading to the loss of control of the discharge.

Experimental investigation on n-decane plasma cracking in an atmospheric-pressure argon environment

In order to solve the problem of the difficulty of igniting and steadily propagating a continuous rotating detonation engine when using liquid hydrocarbon fuel, an experiment was carried out using a dielectric barrier discharge excited by a nanosecond power supply to crack n-decane, the single alternative fuel to aviation kerosene, in a pre-heated argon environment.By changing the voltages and the discharge frequencies, the concentrations of different components as well as a number of different species were acquired.The generating mechanism of olefins and alkanes together with their competition mechanism were acquired.The influence of the voltage on isomer products was also analyzed.The results demonstrate that the bond energy distribution and the species generating condition are the main factors affecting the formation of the products.With the increasing of voltage and discharge frequency, small molecule olefins, large molecular olefins, large molecular alkanes, small molecular alkanes, and hydrogen were detected, and in turn, their concentrations were also increased except for ethylene;what is more, when the voltage was increased over 8.5 kV, the n-butene converted to trans-butene, and the n-pentene converted to isoamylene.

Large Photoluminescence Enhancement by an Out-of-Plane Magnetic Field in Exfoliated WS2 Flakes

We report an out-of-plane magnetic field induced large photoluminescence enhancement in WS2 flakes at 4K,in contrast to the photoluminescence enhancement provided by an in-plane field in general.Two mechanisms for the enhancement are proposed.One is a larger overlap of the electron and hole caused by the magnetic field induced confinement.The other is that the energy difference between varLambda and K valleys is reduced by magnetic field,and thus enhancing the corresponding indirect-transition trions.Meanwhile,the Landé g factor of the trion is measured to be-0.8,whose absolute value is much smaller than normal exciton,which is around-4.A model for the trion gfactor is presented,confirming that the smaller absolute value of the Landé g factor is a behavior of this A–Ktrion.By extending the valley space,we believe this work provides a further understanding of the valleytronics in monolayer transition metal dichalcogenides.

Room-temperature phonon-coupled single-photon emission in hexagonal boron nitride

Photon-lattice(phonon)coupling is fundamental to light-matter interaction,particularly when it reaches the quantum limit of the phonon-coupled single-photon emission,which holds great potential for quantum manipulation and quantum information transduction.Here,we report single defect state-phonon coupling in hexagonal boron nitride(h BN)at room temperature.An ultrabroad spectrum of single-photon emissions can be achieved by selecting the excitation energies.Using photoluminescence excitation spectroscopy,we observe single-phonon-assisted resonance-enhanced single-photon emission,along with multiple phonon replicas that herald the creation of phonon Fock state.We also develop a transition model to gain insight into the physical process behind the single defect state-phonon coupling.Our work sets the stage for manipulating electron-phonon coupling state with single quantum-level precision at room temperature.

Observation of coupling between zero- and two- dimensional semiconductor systems based on anomalous diamagnetic effects

We report the direct observation of coupling between a single self-assembled InAs quantum dot and a wetting layer, based on strong diamagnetic shifts of many-body exciton states using magneto-photoluminescence spectroscopy. An extremely large positive diamagnetic coefficient is observed when an electron in the wetting layer combines with a hole in the quantum dot; the coefficient is nearly one order of magnitude larger than that of the exciton states confined in the quantum dots. Recombination of electrons with holes in a quantum dot of the coupled system leads to an unusual negative diamagnetic effect, which is five times stronger than that in a pure quantum dot system. This effect can be attributed to the expansion of the wavefunction of remaining electrons in the wetting layer or the spread of electrons in the excited states of the quantum dot to the wetting layer after recombination. In this case, the wavefunction extent of the final states in the quantum dot plane is much larger than that of the initial states because of the absence of holes in the quantum dot to attract electrons. The properties of emitted photons that depend on the large electron wavefunction extents in the wetting layer indicate that the coupling occurs between systems of different dimensionality, which is also verified from the results obtained by applying a magnetic field in different configurations. This study paves a new way to observe hybrid states with zero- and two-dimensional structures, which could be useful for investigating the Kondo physics and implementing spin-based solid-state quantum information processing.

Diabolical points in coupled active cavities with quantum emitters

In single microdisks,embedded active emitters intrinsically affect the cavity modes of the microdisks,resulting in trivial symmetric backscattering and low controllability.Here we demonstrate macroscopic control of the backscattering direction by optimizing the cavity size.The signature of the positive and negative backscattering directions in each single microdisk is confirmed with two strongly coupled microdisks.Furthermore,diabolical points are achieved at the resonance of the two microdisks,which agrees well with theoretical calculations considering the backscattering directions.Diabolical points in active optical structures pave the way for an implementation of quantum information processing with geometric phase in quantum photonic networks.

Anisotropies of the g-factor tensor and diamagnetic coefficient in crystal-phase quantum dots in InP nanowires

Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing.In this context,unveiling the fundamental parameters of the crystal phase structure is of much relevance for several applications.Here,we report on the anisotropy of the g-factor tensor and diamagnetic coefficient in wurtzite/zincblende(WZ/ZB)crystal-phase quantum dots(QDs)realized in single InP nanowires.The WZ and ZB alternating axial sections in the NWs are identified by high-angle annular dark-field scanning transmission electron microscopy.The electron(hole)g-factor tensor and the exciton diamagnetic coefficients in WZ/ZB crystal-phase QDs are determined through micro-photoluminescence measurements at low temperature(4.2 K)with different magnetic field configurations,and rationalized by invoking the spin-correlated orbital current model.Our work provides key parameters for band gap engineering and spin states control in crystal-phase low-dimensional structures in nanowires.

Single-electron pumping in a ZnO single-nanobelt quantum dot transistor

Diluted magnetic semiconductors(DMSs)have traditionally been employed to implement spin-based quantum computing and quantum information processing.However,their low Curie temperature is a major hurdle in their use in this field,which creates the necessity for wide bandgap DMSs operating at room temperature.In view of this,a single-electron transistor(SET)with a global back-gate was built using a wide bandgap ZnO nanobelt(NB).Clear Coulomb oscillations were observed at 4.2 K.The periodicity of the Coulomb diamonds indicates that the Coulomb oscillations arise from single quantum dots of uniform size,whereas quasi-periodic Coulomb diamonds correspond to the contribution of multi-dots present in the ZnO NB.By applying an AC signal to the global back-gate across a Coulomb peak with varying frequencies,single-electron pumping was observed;the increase in current was equal to the production of electron charge and frequency.The current accuracy of about 1%for both single-and double-electron pumping was achieved at a high frequency of 25 MHz.This accurate single-electron pumping makes the ZnO NB SET suitable for single-spin injection and detection,which has great potential for applications in quantum information technology.